1. Field of the Invention
The present invention relates to a human body sensing device using an infrared sensor, and more particularly to a human body sensing device for sensing an infrared ray emitted from the human body and sensing the human body's position, based on the sensed infrared ray and a method for fabricating the same.
2. Description of the Prior Art
Generally, HgCdTe infrared sensors being commonly used have a high sensitivity and few errors. By virtue of such characteristics, they are employed in artificial satellites and for the military purpose of watching the movements of the enemy. The infrared sensors are also used for checking defects of machinery and realizing thermal images by measuring a temperature distribution without contact.
On the other hand, pyro-electric infrared sensors being mainly used as unit devices exhibit a small wavelength dependency as compared to the HgCdTe infrared image sensors. They can operate at a room temperature and are very economical. By such characteristics, they are employed for crime prevention and in automatic doors to determine the presence of the human body.
In spite of the above-mentioned advantages, the ultra-electrical type infrared sensors have been used only for limited purposes. This is because the ultra-electrical type infrared sensors have a sensitivity lower than 1/10 of that of the HgCdTe infrared image sensors. As a result, the ultra-electrical type infrared sensors could not be used for military purposes requiring high accuracy.
Referring to FIG. 1, there is illustrated an infrared sensor employed in a human body sensor of a general type. As shown in FIG. 1 , the human body sensor comprises a manganese oxide (MgO) substrate 1 and a dielectric film 2 formed by depositing a ferroelectric thin film such as PbTiO.sub.3 over the MgO substrate 1 by use of a sputtering process and then partially etching the ferroelectric thin film to obtain a patterned structure.
At both lateral ends of the dielectric film 2, support members 3 made of polyimide are disposed on the MgO substrate 1. An upper electrode 4 made of a material having a high conductivity such as Au is disposed on the dielectric film 2.
A lower electrode 5 is disposed on a surface of the MgO substrate 1 opposite to the surface on which the dielectric film 2 and the prior art upper electrode 4 are disposed. The lower electrode 5 is formed by anisotropically etchting the surface of the MgO substrate 1 opposite to the surface including the dielectric film 2 and the upper electrode 4 by use of a wet etching process so as to leave the dielectric film 2 supported by the polyimide support members 3 and then depositing nickel-chromium alloy over a region where the dielectric film 2 remains.
In other words, the human body sensing device comprises the polyimide layer 3 formed on the upper surface of the MgO substrate 1, the dielectric film 2 interposed between the MgO substrate 1 and the polyimide layer 3, an upper electrode 4 formed on both the dielectric film 2 and the polyimide layer 3, and the lower electrode 5 formed on the lower surface of the MgO substrate 1.
When an infrared ray is applied to the infrared sensor having the above-mentioned structure, it is absorbed by the lower electrode 5 and converted into a heat by which an electric charge difference occurs between both surfaces of the dielectric film 2. As a result, a potential difference occurs between the upper electrode 4 and the lower electrode 5.
This potential difference between the upper electrode 4 and the lower electrode 5 is then converted into a capacitor voltage which is, in turn, amplified. The amplified capacitor voltage is treated to be converted into an image.
As mentioned above, however, the infrared sensing device has a degradation in performance in that a dielectric material having a high sensitivity is not be readily available, that even though a high-sensitive dielectric material is available, it is irregularly deposited, and that an error is generated due to a thermal interference among sensors.